I am new to the forum, but not to shooting. I have a 270 WBY Mag, Mark V Sporter, sitting in the closet taking up space. I am considering another long range gun and wanted to turn this into a custom. I am looking for something unique, however, easy to convert. I understand for the most part WBY's case are some what similar and would be easy to go up or down in caliber. Not that there is anything wrong with the 270, however, not something I want any more. The rifle means to much to me to get rid of it. I would imagine the .257 would be a nice conversions or go on the high end of a 7mm/300. I currently shoot a .300 Remington Ultra Mag which is very accurate, so I do not know if I want another of that similarity. If I were to go on the larger end of calibers, I am looking at the 338 Laupa! So I don't know, I am just throwing it out there for some other insight!

Thanks for your help!

Been around the .257 mag a lot, and own a .270 mag. I like the 270 much better. It's similar to the .264 Win mag in case size, and that's way overbore for a 6.5 bullet. On the other hand the 7mm remington mag is slightly shorter than the .270 mag case if that matters much. But a 7mm Weatherby mag is basicly the same case as the .270 mag. It will push a 150 grain bullet 300fps faster than the Remington, and a 160 grain bullet 200 fps faster. You can run a neck expander thru the .270 cases and make 7mm Weatherby mag brass.

So you are saying make my 270 WBY Mag into a 7MM WBY Mag? You think the 7mm Wby Mag has better ballistics than the 257WBY Mag? Im not against that, however, I already have a large magnum round in my 300 RUM!

Ballistically the Lapua isn't WAY better than the 340WBY, the superior brass IMHO, is what makes the difference. (not to mention the beltless case). Heck, if you have the MK5 action, lets go with an allen Mag of some sort!!! might as well let it all hang out.

if it's Weatherby branded brass, then it's made by Norma. And lets face it Norma brass isn't exactly bad brass (some folks like it just as well as Lapua). The 6.5/300 mag is way way overbore, as the .264 Win mag shows right now (a lot of the problems are once again due to a poor shoulder and neck design). The .270 Weatherby shoulder angle computes to about 48 degrees just like the 7mm WBY mag. add that with the very long neck, and you'll be able to use very long bullets without the base being down in the shoulder area (note nobody says you gotta have a lot of free bore with either of these two rounds).

Ackley said that the 6.5-06 was about all the powder the 6.5 could use efficiently unless you went with big heavy bullets. That's why the gains with the 6.5-06AI are not as much as most folks expect to see. I would expect that the 6.5 / 7mm weatherby mags with a lot less free bore would make very fine 1000 yards shooters. The .300 mag is already known to be a top performer in that class of shooting
gary

So you are saying make my 270 WBY Mag into a 7MM WBY Mag? You think the 7mm Wby Mag has better ballistics than the 257WBY Mag? Im not against that, however, I already have a large magnum round in my 300 RUM!

Long range wise I'd pick it. But if your thinking 600 yards or less the .257 will get it done. The problem with the .257 bore is the complete lack of good bullets, and the well known fact that the .257 WBY mag is way overbore. With that case it takes about 140 grains or heavier to really see a lot of difference. The 140 grain bullet in the 270 mag will go almost as fast as the 115 grain bullet in the .257, and that ought to tell us all something. The 150 grain bullet in the 7mm mag is only about 150 fps slower with much better ballistics. A 117 grain Hornaday SST has about .390B/C while the 162 grain Hornaday has a .550B/C at about 200fps slower velocity. My charts don't list a 3200fps with a .55B/C, so I used a .54B/C at 3100fps. That's not even close!

The 257, 270 and 7mm wby's are all the exact same case. So you can interchange any of those with your magazine and bolt throw the same as it is now.

It depends on what you want to do with it. For a lights out flat shooting deer rifle to 650 yards or so it is hard to beat a 257 wby shooting a 100 grain bullet 3750+ fps. My load with the 100 grain hits 3760 fps and regularly shoots groups under 2" at a quarter mile. My son shot a 2" 600 yards group last year with it getting ready for his antelope hunt. It is an off the shelf mk 5 wby rifle.

I have shot the 270 and 7mm wby's long range for 35 years. The better bc's in 7mm are why it is a better choice. The 7mm-300 wby was extremely popular as a hunting round and 1000 yard rifle back in the 70's setting 1000 yard world records. It is 200+ fps faster than the standard 7mm wby. Remington coming out with the 8mm rem mag in 1977 making cheap brass available caused the 7mm-300 wby to lose popularity. Necking the 8mm remington gave the same ballistics with cheap brass. After that wildcat became extremely popular for about 20 years Layne Simpson decided to pull his weight with his magazine and make it a standard cartridge giving it the magazine name, shooting times westerner or STW.

I have several of the 257, 264 and 7mm STW's and they are all top shooters and way fun to shoot. The ballistics of the 264 STW are among the best in the business for long range shooting to 1000 yards or so. It can drive the 140 Berger to 3400 fps making it a super long range deer/antelope cartridge. I have one with near 1000 rounds on it and it seems to just get better with age. As newer powders become available the 264 STW just keeps getting better and is one of my all time favorites since before anyone ever heard the wildcat called an stw.

If I had to pick a super long range deer/antelope cartridge it would be the 264 STW because a brake is not needed for pushing the little 140's where it is needed in 7mm pushing high bc bullets. The 6.5 STW with 140 grainers will ballistically outshoot the 7mm STW with 168 grainers.

If I had to pick a long range elk rifle it would be the 338-378 wby. It basically just blows away the competition in a hunting weight rifle and makes hits at long range far easier than with the little stuff off the RUM and Lapua cases. You can use the strong Lapua brass and push it hard to try and get close to the 338-378 wby with an improved Lapua or just shoot faster safely and easily with the 338-378 wby.

So, there are my two rifles for long range hunting weight rifles and I own or have built or shot at my range about everything talked about on this forum with hands on experience.

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